1. Field of the Invention
This invention relates generally to the field of hard disc drives and more particularly, but not by way of limitation, to a system for attaching the head/flexure assemblies to mounting arms on the actuator of the disc drive.
2. Brief Description of the Prior Art
Disc drive data storage devices of the type known as "Winchester" disc drives are well known in the industry. Such disc drives incorporate one or more rigid discs coated with a magnetizable medium to store digital information on a plurality of circular, concentric tracks. The recording and retrieval of data--also referred to as writing and reading, respectively--is accomplished through the use of an electromagnetic transducer carried in a slider body having a self acting hydrodynamic air bearing which "flies" the device above the disc surface. This combination is sometimes referred to collectively as a head. An actuator is used to controllably move the heads from track to track, under control of electronic circuitry.
While the present invention is suitable for use with any type of actuator, the type of actuator most commonly used in hard disc drives of the present technology is the rotary voice coil actuator. In a rotary voice coil actuator, a voice coil motor (VCM) is coupled through a pivot mechanism to an array of vertically aligned heads. The pivot mechanism typically includes an actuator body with the VCM coil attached to one side and a plurality of head mounting arms projecting from the opposite side. The heads are mounted to the head mounting arms via flexures which encourage the heads into proper cooperative arrangement with the spinning discs and allow small variations in the roll and pitch attitudes of the heads to conform to minute variations in the disc surfaces. Such flexures are described in detail in U.S. patent application Ser. No. 07/975,352, filed Nov. 12, 1992, and assigned to the assignee of the present invention.
The above-cited application notes that many schemes have been set forth for mounting the flexure to the actuator in the disc drive, and that almost all involve the welding of the flexure--typically made of thin stainless steel--to a thicker, more substantial mounting plate. This is because the thin material of the flexure itself is usually not adequate to absorb the types and amounts of stresses needed to securely attach the flexure to the actuator.
One type of common prior art scheme used to mount the flexure to the actuator using one or more machine screws or bolts to attach the mounting plate of the flexure to the head mounting arm of the actuator. Such a method is described in U.S. Pat. No. 4,167,765 (Watrous), and is advantageous in applications where head/gimbal assembly (HGA) failures occur frequently during manufacturing testing of the disc drive and HGA replacement is common. This type of attachment scheme does have several drawbacks:
1. it is generally expensive, due to the costs associated with drilling and tapping threaded holes in the head mounting arm and the cost of miniature machine screws, PA0 2. it generally requires that the head mounting arms be of a design wherein the arms themselves must be attached to the actuator body using screws, further increasing cost and complexity of assembly, PA0 3. it is commonly susceptible to unacceptable variations in geometry brought about by differential thermal expansion across the temperature range specified for the disc drive, and PA0 4. it is generally unsuitable for applications in which the spacing between the discs is small since the heads of the screws tend to contact the disc surfaces.
Another type of head mounting widely used is the "swage mount", such as that described in U.S. Pat. No. 4,875,117 (Slezak, Levy). In such a scheme, the mounting plate that is welded to the flexure includes a hollow, cylindrical protrusion, called a "boss" on one side. The boss fits intimately into a hole in the head mounting arm, and a staking ball--or similar device--is forced through the boss to deform the boss outwardly into contact with the inner surface of the hole in the head mounting arm. This type of design eliminates the need for removable head mounting arms, as well as the tapped holes and miniature machine screws, the lack of which is desirable in low cost disc drives. However, the mounting plate itself can be excessively expensive. Strong, high quality mounting plates must be made on screw machine lathes. Plates made on a stamping press are less expensive, but more prone to excessive distortion during the swaging process, and this distortion may change the intended force the flexure is to furnish against the slider, which will in turn affect the flying height of the slider and the reliability of the disc drive. Moreover, such distortion can lead to high stresses which will cause cracking of the mounting plate, the head mounting arm, or both. Furthermore, removal of HGAs from the head mounting arms is difficult with this type of design, and the head mounting arm through-hole is deformed during the swaging process. Lastly, this design, too, does not lend itself to applications where disc-to-disc spacing is small. The mounting plate bosses must be of a certain minimal length to ensure adequate overlap of the boss and head mounting arm material, the head mounting arm must be of sufficient thickness for adequate strength should such flaws as casting porosity be present in the arm, and the "stacking" of the mounting plates on top and bottom of the head mounting arm adds vertical height.
An alternative swage mounting scheme has been suggested in U.S. patent application 07/639,136, filed Jan. 1, 1991 abandoned, now continuation application Ser. No. 07/925,324, filed Aug. 6, 1992, where separate holes in the head mounting arm are provided for the HGAs on opposite sides of the head mounting arm, but the cost of the increased complexity of the mounting plate argues against this scheme.
Attachment of the flexure to the head mounting arm by adhesives has also been attempted, but is not favored due to the variability of adhesive quality and the tendency of the HGAs to "drift" on the head mounting arm, resulting in mis-registration of the head transducers relative to the data tracks.
Attachment of the flexure to the head mounting arm by one or more rivets has been described in U.S. Pat. 4,783,710 (Salyer, Toor) and IBM Technical Disclosure Bulletins volume 28, number 6, page 2453 and volume 29, number 1, page 256. These types of mounting schemes are similar to the screw types described above, except the screws have been replaced with less expensive rivets. This reduces cost, but makes replacement of HGAs more difficult and as a result is less widely used.
It has also been proposed to weld the flexure directly to the head mounting arm but, in general, this cannot be done, since the flexures are typically made from 300 series stainless steel and the head mounting arms are commonly either aluminum or magnesium. While the head mounting arms could be made of stainless steel to facilitate such welding, this would greatly increase the mass and inertia of the actuator, resulting in a slower movement of the heads from track to track.
Elimination of the mounting plate has also been investigated but abandoned, since it has been found that, to maintain an invariant flexure force through the various steps in manufacturing, it is best to have the flexure welded to a stiff, rigid plate.
Therefore, it can be seen that a low cost, easily manufactured mounting scheme for mounting the flexure to the head mounting arms is desirable, and such a mounting scheme would be of the greatest benefit if it also contributed to the minimization of the disc-to-disc spacing in a disc drive.